The instant invention relates to a process for forming a deposit on the surface of a metallic or conductive surface. The process employs an electrolytic process to deposit, for example, a mineral containing coating or film upon a metallic, metal containing or an electrically conductive surface.
Silicates have been used in electrocleaning operations to clean steel, tin, among other surfaces. Electrocleaning is typically employed as a cleaning step prior to an electroplating operation. Using xe2x80x9cSilicates As Cleaners In The Production of Tinplatexe2x80x9d is described by L. J. Brown in February 1966 edition of Plating; hereby incorporated by reference.
Processes for electrolytically forming a protective layer or film by using an anodic method are disclosed by U.S. Pat. No. 3,658,662 (Casson, Jr. et al.), and United Kingdom Patent No. 498,485; both of which are hereby incorporated by reference.
U.S. Pat. No. 5,352,342 to Riffe, which issued on Oct. 4, 1994 and is entitled xe2x80x9cMethod And Apparatus For Preventing Corrosion Of Metal Structuresxe2x80x9d that describes using electromotive forces upon a zinc solvent containing paint; hereby incorporated by reference.
The instant invention solves problems associated with conventional practices by providing a cathodic method for forming a protective layer upon a metallic or metal containing substrate (e.g., the protective layer can range from about 100 to about 2,500 Angstroms thick). The cathodic method is normally conducted by contacting (e.g., immersing) a substrate having an electrically conductive surface into a silicate containing bath or medium wherein a current is introduced to (e.g., passed through) the bath and the substrate is the cathode.
The inventive process can form a mineral layer comprising an amorphous matrix surrounding or incorporating metal silicate crystals upon the substrate. The characteristics of the mineral layer are described in greater detail in the copending and commonly assigned patent applications listed below.
An electrically conductive surface that is treated (e.g., forming the mineral layer) by the inventive process can possess improved corrosion resistance, increased electrical resistance, heat resistance, flexibility, resistance to stress crack corrosion, adhesion to topcoats, among other properties. The treated surface imparts greater corrosion resistance (e.g., ASTM B-117), among other beneficial properties, than conventional tri-valent or hexa-valent chromate systems. The inventive process can provide a zinc-plate article having an ASTM B-117 resistance to white rust of at least about 72 hours (and normally greater than about 96 hours), and resistance to red rust of at least about 168 (and normally greater than about 400 hours). The corrosion resistance can be improved by using a rinse and/or applying at least one topcoating.
The inventive process is a marked improvement over conventional methods by obviating the need for solvents or solvent containing systems to form a corrosion resistant layer, e.g., a mineral layer. In contrast, to conventional methods the inventive process can be substantially solvent free. By xe2x80x9csubstantially solvent freexe2x80x9d it is meant that less than about 5 wt. %, and normally less than about 1 wt. % volatile organic compounds (V.O.C.s) are present in the electrolytic environment.
The inventive process is also a marked improvement over conventional methods by reducing, if not eliminating, chromate and/or phosphate containing compounds (and issues attendant with using these compounds such as waste disposal, worker exposure, among other undesirable environmental impacts). While the inventive process can be employed to enhance chromated or phosphated surfaces, the inventive process can replace these surfaces with a more environmentally desirable surface. The inventive process, therefore, can be xe2x80x9csubstantially chromate freexe2x80x9d and xe2x80x9csubstantially phosphate freexe2x80x9d and in turn produce articles that are also substantially chromate (hexavalent and trivalent) free and substantially phosphate free. The inventive process can also be substantially free of heavy metals such as chromium, lead, cadmium, cobalt, barium, among others. By substantially chromate free, substantially phosphate free and substantially heavy metal free it is meant that less than 5 wt. % and normally about 0 wt. % chromates, phosphates and/or heavy metals are present in a process for producing an article or the resultant article. In addition to obviating chromate containing processes, the inventive method forms a layer having greater heat resistance, flexibility, among other properties, than conventional chromate coatings. The improved heat resistance broadens the range of processes that can be performed subsequent to forming the inventive layer, e.g., heat cured topcoatings, stamping/shaping, riveting, among other processes.
In contrast to conventional electrocleaning processes, the instant invention employs silicates in a cathodic process for forming a mineral layer upon the substrate. Conventional electro-cleaning processes sought to avoid formation of oxide containing products such as greenalite whereas the instant invention relates to a method for forming silicate containing products, e.g., a mineral.
The subject matter of the instant invention is related to copending and commonly assigned WIPO Patent Application Publication No. WO 98/33960, Non-Provisional U.S. Patent Application Ser. No. 08/850,323 (Now U.S. Pat. No. 6,165,257); Ser. No. 08/850,586 (Now U.S. Pat. No. 6,143,420); and Ser. No. 09/016,853 (now allowed), filed respectively on May 2, 1997 and Jan. 30, 1998, and Ser. No. 08/791,337 (now U.S. Pat. No 5,938,976), filed on Jan. 31, 1997, in the names of Robert L. Heimann et al., as a continuation in part of Ser. No. 08/634,215 (filed on Apr. 18, 1996) in the names of Robert L. Heimann et al., and entitled xe2x80x9cCorrosion Resistant Buffer System for Metal Productsxe2x80x9d, which is a continuation in part of Non-Provisional U.S. Patent Application Ser. No. 08/476,271 (filed on Jun. 7, 1995) in the names of Heimann et al., and corresponding to WIPO Patent Application Publication No. WO 96/12770, which in turn is a continuation in part of Non-Provisional U.S. Patent Application Ser. No. 08/327,438 (filed on Oct. 21, 1994), now U.S. Pat. No. 5,714,093.
The subject matter of this invention is related to Non-Provisional Patent Application Ser. No. 09/016,849 (Attorney Docket No. EL004RH-1), filed on Jan. 30, 1998 and entitled xe2x80x9cCorrosion Protective Coatingsxe2x80x9d. The subject matter of this invention is also related to Non-Provisional Patent Application Ser. No. 09/016,462 (Attorney Docket No. EL005NM-1), filed on Jan. 30, 1998 and entitled xe2x80x9cAqueous Gel Compositions and Use Thereofxe2x80x9d (now U.S. Pat. No. 6,033,495). The disclosure of the previously identified patents, patent applications and publications is hereby incorporated by reference.